1. Field of the Invention
The present invention relates to a method of manufacturing a polyelectrolyte such that ion groups are introduced into polystyrene resin.
2. Description of Prior Art
Polystyrene resin has excellent electric characteristic, satisfactory rigidity and sufficient water resistance while exhibiting low costs. Therefore, the polystyrene resin is solely or formed into an alloy combined with a copolymer or another resin so as to be used in buffers (foamable styrol), packing materials, electric products and frames and various parts for automobiles. Thus, the polystyrene resin is a general-purpose resin considered equal to polyolefin resin represented by polyethylene.
In addition to the purpose of the polystyrene resin for use as the structural material, the polystyrene resin is refined into a polyelectrolyte so as to be used as coagulant for waste water treatment, an additive for cement, a material for fluidizing coal slurry, dispersant for inorganic pigment, a material for reinforcing paper, a surface sizing material for paper, a conductive material for an electronic copying machine, a destaticizer, a scale preventive material, dispersant for emulsion polymerization and aqueous glue and the like.
To refine the polystyrene resin into a polyelectrolyte, for example, a method may be employed in which sulfonate or an amine salt subjected to a chloromethylation process is introduced into the polystyrene resin so that the polystyrene resin is formed into a water-soluble polymer.
However, an actual process for refining the polystyrene resin into a polyelectrolyte encounters a variety of problems.
For example, sulfonation of the polystyrene resin, which is performed in a sulfonating agent, requires a large quantity of the sulfonating agent, represented by concentrated sulfuric acid. Moreover, the large quantities of the sulfonating agent and water for cleaning the sulfonating agent are discharged after the reactions have been performed. Thus, there arises a problem in that resources cannot be saved, the waste cannot be reduced and the manufacturing cost cannot be reduced. If the sulfonating operation is performed as described above, molecule crosslinking (sulfon crosslinking) easily occur when reactions are performed. Thus, the polymers are allowed to gel and therefore unnecessary polymers can easily be formed in water. Moreover, the foregoing gelation becomes apparent in proportion to the molecular weight of the polymer and the molecule chains of the polymers can easily be cut. Therefore, a high molecular polyelectrolyte cannot easily be obtained.
When the sulfonating reactions are performed in a chlorine solvent, a large quantity of the chlorine solvent remains in the polyelectrolyte after subjected to the reactions and its water solution. As a result, halogen compounds are contained in the polyelectrolyte product. Therefore, if the foregoing polyelectrolyte is used in the coagulant for waste water treatment, dispersant for cement, absorbing resin, a surface sizing material for paper or the like, the halogen compounds are discharged into waste water. Thus, the foregoing polyelectrolyte cannot practically be employed because of difficulty to satisfy a waste water regulation.
Since the molecular weight (Mw) of the thus obtained polyelectrolyte is generally 150,000 to 600,000, a polyelectrolyte having a large molecular weight has been required to improve the performance when the polyelectrolyte is used as, for example, a coagulant.
Since the sulfonating reaction encounters reduction in the reaction rate if water is contained in the system, water must completely be removed to again use the solvent in the reactions.
However, a conventional technique, for example, still standing separation, involves a fact that sulfonated substances of aromatic polymers, which are reaction products, serve as surface active agents. Thus, the boundary between the aqueous layer and the solvent layer becomes confused, thus causing the separation to be made difficult. When the solvent is recovered by distillation, the solvent of the chlorine type hydrocarbon and water form azeotropic mixture. Complete removal of water from the solvent cannot easily be realized, thus causing a necessity for performing refining and dehydration processes to arise.
Therefore, there arises problems in that the working efficiency deteriorates and new additional facility is required.
What is worse, the polystyrene resin has a problem of a halogen flame retardant.
Since the halogen flame retardant has a significant flame retardant effect with respect to a variety of plastic materials and its cost is very low, the halogen flame retardant is used widely over the world.
However, use of the halogen flame retardant raises a problem because the halogen flame retardant generates halogenated hydrogen when it burns. In particular, use of decabromodiphenyl oxide (DBDPO), which is used most widely and which generates toxic substances, such as dioxine, has been regulated.
The halogen flame retardant, having excellent flame retardant effect with respect to aromatic resins represented by styrene resin, are widely used in the frames of home electronic products and as a material of parts.
Therefore, if the home electronic products are dumped, a large quantity of plastic substances containing the halogen flame retardant are discharged.
The plastic wastes are usually burnt or reclaimed except for a small portion which is recycled by heating and melting.
When the plastic wastes are attempted to be disposed by burning, the above-mentioned problem of generation of toxic gases arises. Therefore, the disposal must be performed by the reclamation at present.
The amount of plastic wastes containing the halogen flame retardant has been enlarged year by year. Therefore, the reclamation disposal is ineffective and thus there arises a critical problem for Japan considerably wanting of reclamation plants.
If recycling of plastic wastes is attempted, recycle of the plastic containing the halogen flame retardant, the use of which is regulated, is not preferable.